This invention relates to a starter apparatus with a planetary speed reduction gear and, more particularly, to a starter apparatus with a planetary speed reduction gear in which the rotation of a d.c. electric motor is transmitted through a planetary speed reduction gear mechanism to a pinion for driving an engine ring gear.
FIGS. 7 to 9 illustrate a conventional starter apparatus 1 with a planetary speed reduction gear, and the starter apparatus 1 comprises a d.c. electric motor 2, an over-running clutch 4 slidably placed over an output rotary shaft 3 connected to an armature rotary shaft of the d.c. electric motor 2 and a planetary speed reduction gear mechanism 5 which transmits, after speed-reducing, the rotational force of the armature rotary shaft through the output rotary shaft 3 to a clutch outer member of the over-running clutch 4. A shift lever 6 is provided to be driven by an unillustrated solenoid switch to cause a pinion 7 mounted to the output rotary shaft 3 to engage and disengage with respect to the engine ring gear.
The planetary speed reduction gear mechanism 5 comprises an internal gear 10 made of a resin material and mounted to a housing 9 disposed on a front bracket 8, a spur gear 11 mounted to an armature rotary shaft and a plurality of planetary gears 12 in engagement with the internal gear 10 and the spur gear 11, and a planetary gear carrier 13 pivotally supporting the planetary gears 12 is connected to the output rotary shaft 3. Disposed between the d.c. motor 2 and the internal gear 10 is a packing 14.
With the above conventional starter apparatus, the rotation of the armature rotary shaft is transmitted from the spur gear 11 to the planetary gears 12 and is speed-reduced by the planetary speed reduction gear mechanism 5 to be transmitted to the over-running clutch 4. Therefore, the pinion 7 which is in engagement with the over-running clutch 4 is rotated and moved forward to engage and drive an unillustrated engine ring gear.
In the conventional planetary speed reduction gear starter apparatus as above-described, the internal gear deforms into a shape approximating a polygon having a number of sides corresponding to the number of planetary gears when a massive load is applied to the planetary speed reduction gear mechanism. Under such circumstances, the engagement between the planetary gears and the internal gear is shallow and the contact surface pressure is increased, so that the teeth of the gears are broken and the dedendum stress is increased because of the concentrated load on the tip of each tooth.